1. Field of the Invention
The present invention relates to a method of forming a phosphor film, and more particularly to a method of forming a phosphor film used in fluorescent displays of a field emission device and display panel.
2. Description of the Related Art
Generally, a phosphor film is widely used in various fluorescent displays of field emission devices and plasma display panels. Techniques relating to such a phosphor film are broadly divided into techniques pertaining to phosphor materials and film formation techniques. In particular, the most important factor in the phosphor film formation technique is uniform distribution of phosphor components in the formed film and their adhesivity to a substrate.
As conventional phosphor film formation techniques, there are, broadly speaking, methods of forming a film using a binder, such as screen printing and spraying, and vapor deposition methods using no binder such as PLD, MOCVD and ALE. Generally, the vapor deposition method as a phosphor film formation process, suffers from a very limited range of applicable phosphor materials, difficulty in realizing a large area required in the devices of interest, and high production cost, thus failing to reach commercialization.
Due to those problems, present commercial phosphor film formation techniques are, broadly speaking, a screen printing process and a spraying process, using the binder. As the representative phosphor film formation technique, the screen printing process is initiated with preparation of phosphor paste by mixing phosphor powder and an organic binder in a solvent. Next, a screen 12 (also, referred to as mesh) is placed on a substrate 11, as shown in FIG. 1, and then the phosphor paste 15 is printed on the substrate 11 through the screen 12 by using a scrubber 14. The phosphors 16 printed on the substrate 11 are heat treated to remove solvent and some of the binder and thereby the desired phosphor film can be formed.
The phosphor film formation technique using the above-mentioned screen printing process requires an additional heat treatment process in order to remove the binder and solvent, and has problems such as deterioration of fluorescence efficiency due to the remaining binder even after heat treatment. In severe cases, the binder decomposes at a high driving voltage, resulting in local falling down of the phosphor film. Meanwhile, where less amount of the binder is used or removing rate of the binder is increased in order to cope with problems associated with the remaining binder, it may rather weaken adhesivity between the substrate and phosphor film and then lead to fatal defects of products. Further, when the field emission device is driven, remaining gas seeps out of the binder inside the field emission system that is under vacuum thus reducing light emitting life span. Therefore, conventional processes using the binder have fundamental problems, and the spraying process using the binder also suffers from those problems.
Further, the conventional screen printing process has disadvantages in that agglomerates occurred due to failure of dispersion into phosphor paste or slurry remain in the phosphor film, thus causing reduction of fluorescence efficiency. In addition, when forming the thin phosphor film, it is difficult to precisely control uniform film thickness unlike the conventional vapor deposition.
Therefore, there remains a need in the art for a new phosphor film formation technique that is suitable for mass production while improving adhesion between the phosphor film and substrate, and fluorescence efficiency and light emitting life span by solving problems due to the binder.